This disclosure relates to an electromechanical actuator lubrication system used for a ram air turbine (RAT), for example.
A typical hydraulic RAT actuator includes a piston rod movable relative to a cylinder. In one example actuator, the piston rod is affixed to a housing. The housing includes a long nose that is machined as part of the housing. The cylinder slides axially relative to the nose during deployment.
Historically, this nose has been designed such that no high pressure oil, generated during the damping motion of the actuator, escapes during the deployment of the RAT. A cavity is provided between the nose and the cylinder and housing. This cavity is typically filled with return pressure oil from the aircraft. Several recent aircraft designs employ check valves in the hydraulic system upstream of the RAT to prevent loss of hydraulic oil in the event of a catastrophic event. Therefore, when the actuator tries to draw fluid upon deployment it can create a vacuum in the system. This vacuum is eventually filled by leakage from other various flight control components.
The return pressure is typically relatively low, however, the pressure has increased significantly on recent aircraft designs. Only one dynamic seal maintains the oil-filled cavity, and there is a possibility that fluid might leak from the cavity, which is undesirable. Moreover, there is a chance that the cylinder may become misaligned relative to the nose since the nose is fixed relative to the cylinder, which could provide a leak path.